At present, the impedance problem that the whole circuit is used as a power supply load is required to be considered without exception in designs and tests in the filed of electronic circuits and electromagnetic compatibility. Taking authentication of electromagnetic compatibility as an example, when a product supplier obtains international authentication, both radiated emission and conducted emission are compulsory test items. It is well known that electromagnetic interference in a power supply part (a frequency band of 30 MHz-60 MHz) is a very important factor that influences test results, such as radiated emission and conducted emission. A common practice is to simulate the designed circuit, perform assessment tests constantly and then check omissions and make up deficiencies according to the test results, or replace devices, or modify printed circuit boards (PCB). Thus, the whole development period of the whole product is prolonged, costs are greatly increased and design effects are unsatisfactory. Although most of current power suppliers add a typical Electromagnetic Interference (EMI) filter in a power supply module, the effect is commonly not ideal. A main reason is that in the prior art, load impedance on which setting of parameters of the EMI filter is based is obtained through a simulation method and is a theoretical value. Thus, the impedance of the typical EMI filter is not matched with the load impedance such that frequency bands or frequency points filtered out by the filter are not at all frequency bands or frequency points that are expected to be filtered out.